1. Field of the Invention
This invention relates to electrophotographic image forming apparatus, and more particularly to cleaning devices for removing residual toner and debris from a charge retentive surface of an image forming device.
2. Description of Related Art
In electrophotographic applications such as xerography, a charge retentive surface of a photoreceptor is electrostatically charged, and exposed to a light pattern of an original image to be reproduced, to selectively discharge the photoreceptive surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as toner. Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original beam reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. The process is well known, and is useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Multicolor electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoreceptor, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complimentary thereto. This process is repeated in a plurality of cycles for differently colored images and their respective complimentary colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multilayered toner image on the copy sheet. Thereafter, the multilayered toner image is permanently affixed to the copy sheet as described above to create a color copy. The developer material (toner) may be a liquid material or powder material.
Although, a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface of the photoreceptor, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, toner additives, kaolins and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimal imaging that the toner and debris remaining on the surface be cleaned thoroughly therefrom.
The quality of images produced by such equipment depends significantly on the ability to clean the photoconductive surface before it is reused.
Blade cleaning is a highly desirable method for removal of residual toner and debris (hereinafter, collectively referred to as "toner") from a photoreceptor. In a typical application, a relatively thin elastomeric blade member is provided and supported adjacent to and transversely across the photoreceptor surface with a blade edge chiseling (doctor mode) or wiping (wiper mode) toner from the surface. Subsequent to release of toner from the surface, the released toner accumulating adjacent to the blade is transported away from the blade area by a toner transport arrangement, or by gravity.
However, the blades are subject to wear and thus must be replaced. The need for replacement is unpredictable and usually requires a technician.
Accordingly, to simplify blade replacement and minimize technician service, a need exists for a multiple blade apparatus for cleaning residual toner and debris from the moving charge retentive surface of an image forming apparatus, such that the blade holder of the multiple cleaning blade indexing apparatus is capable of positioning, loading and aligning each blade within allowable tolerances (as known in the art, tolerances are determined separately for applicable electrophotographic apparatuses). That is, the blade angle to the photoreceptor, blade load against the photoreceptor and alignment of the blade edge to the photoreceptor must be within operational tolerance zones. Further, the blade angle and blade load requirements demand that the blade be locked into position after indexing, and the blade edge alignment requirement dictates that the blade must be free to pivot and align itself to the photoreceptor plane with no interference from the indexing mechanism.
A number of cleaning apparatuses for photoreceptors which employ a cleaning blade are known.
U.S. Pat. No. 5,081,505, to Ziegelmuller et al., discloses a rotatable wiper blade roller for cleaning residual toner particles from an image bearing surface and includes a plurality of indexable wiper blades. The blades engage the image bearing surface at an angle of 60.degree. to 85.degree. defined in the direction of particle removal by the cleaning edge of each such blade and image-bearing surface. The blades are cleaned secondarily by an intermittently rotatable fur brush that is completely out of contact with the image bearing surface.
U.S. Pat. No. 4,989,047, to Jugle et al., discloses a photoreceptor cleaning apparatus for the reduction of agglomeration caused spotting. A thin scraper member arranged at a low angle to the photoreceptor is provided as a secondary cleaning device to a rotating negatively biased fiber brush which contacts the surface of the photoreceptor upstream of the blade to remove most of the adhering toner particles. The rotating brush removes the preponderance of toner from the photoreceptor, and the blade removes any toner agglomerates formed on the photoreceptor by the agglomeration of toner.
U.S. Pat. No. 4,364,660, to Oda, discloses a photoreceptor cleaning system having a cleaning blade which removes toner from a photoreceptor. A fur brush located upstream of the cleaning blade acts as a toner recovery mechanism to recover toner removed from the photoreceptor by the cleaning blade.
U.S. Pat. No. 4,451,139, to Yanagawa et al., discloses a cleaning apparatus for a photoreceptor which includes an elastic polyurethane cleaning blade located downstream of a rotating fur brush with respect to the rotation direction of the photoreceptor.
U.S. Pat. No. 3,947,108, to Thettu et al., discloses a photoreceptor cleaning system wherein a blade acts as a primary cleaning member. A brush located downstream of the blade removes the residual film from the photoreceptor not removed by the blade.